A scanning electron microscope (SEM) scans a sample located in a vacuum sample chamber with a focused electron beam, and detects secondary electrons or back-scattered electrons among signals generated from the sample, thereby making it possible for a researcher to observe the target sample.
Since an electron is very light, the electron bounces off a gas molecule when colliding with the gas molecule. Thus, when air is present in a body tube, the electron cannot actively move. Therefore, a high vacuum state of approximately 10−4 to 10−10 Torr is maintained in a body tube of an electron microscope or focused ion beam observation equipment.
The vacuum degree of a sample chamber on which an electron beam emitted from the body tube is incident must be maintained at approximately 10−3 Torr. This is because when the sample chamber is maintained in a low vacuum state, gas may flow backward to the body tube maintained in a high vacuum state. Furthermore, when a sample is put into or taken out of the sample chamber, the vacuum of the sample chamber changes to the atmospheric pressure. Therefore, a predetermined waiting time must be taken until the sample chamber reaches a vacuum degree required for observation of the electron microscope. In order to reduce such a waiting time, an auxiliary sample chamber for maintaining the vacuum degree of the sample chamber is suggested.
In a photoelectron microscope for observing a specific portion of an image observed through an optical microscope in more detail, a light source or light detector must be inserted into a sample chamber. Therefore, a structure for maintaining a vacuum state in the sample chamber becomes more complex than a sample chamber of a general electron microscope.
U.S. Pat. No. 8,530,856 discloses an optical microscope including a sample chamber having a valve installed at a portion connected to a body tube. In the related art, however, when a sample is put into or taken out of the sample chamber, the sample chamber cannot maintain a vacuum state. Furthermore, the size of the sample chamber is increased in order to insert a light source or optical body tube into the sample chamber. Thus, a time and cost are required until the sample chamber reaches a vacuum degree.